Technologies suitable for tracking are known, such as satellite systems (GPS, GLONASS), terrestrial GSM type communication networks, local area networks (Bluetooth, Wi-Fi, Zigbee, ULB, Infra-Red, etc.) or inertial platforms.
Techniques for tracking a device using methods based on time measurements (known to those skilled in the art under the terms Time Of Flight (TOF)/Time Of Arrival (TOA), Time Difference Of Arrival (TDOA)), on an angular measurement of the arrival of the wave (Angle of Arrival (AOA)), on the analysis of the strength of a signal received from an antenna by RSSI measurement (RSSI=Received Signal Strength Indicator), wave phase shift or known zone identification are also known.
The equipment required for the methods cited such as the use of landmarks is also known. A landmark is an item of reference equipment of known position suitable for exchanging a set of information with the remote device. The number of these landmarks is dependent on the tracking technique used as well as the context of use.
Tracking by means of triangulation is known, which processes the information from three landmarks, the cognitive independence whereof is assumed. Triangulation uses only angle measurements (AOA) between the landmarks and the signals received.
Tracking by means of trilateration is also known, which requires, like triangulation, three sources of information, the cognitive independence whereof is observed, but which only uses distance measurements. This distance measurement can be implemented in different ways such as by RF fingerprinting, known zone identification methods or methods known as “fingerprinting”. The implementation of these methods requires a learning process liable to render the processing thereof restrictive. Estimation using the time of flight techniques mentioned above (TOA/TOF, TDOA) uses the signal velocity as well as the travel time between transmission and reception of the signal. This solution is subject to the context of use and must account for the type of signal as well as the signal propagation environment; an implementation is described in the document WO 2006/072697 (France Telecom). Some technologies are more suited to these methods than others. For example, ULB (IEEE 802.15.4a) based on the interpretation of TDOA type measurements in indoor environments offers sufficient precision but requires the installation of a considerable infrastructure.
The infrastructures required for each method, the limits of each, according to the study environment as well as the constraints associated with the requirements of use of the solution are also known.
More specifically, there are solutions implementing different technologies which are suitable for tracking an object. Some solutions use an accelerometer, the information whereof is transmitted by a radiofrequency (RF) transmission module. Recently, the technology known as “Bluetooth” has been used to enable communication between a “parent” device and a “child” device.
The document GB 2 349 301 describes the concept of a wireless system suitable for monitoring children, equipped with a transmitter which can be placed in a wristband, using a receiver borne by an adult responsible for monitoring.
U.S. Pat. No. 6,246,379 (Texas Instruments) describes a Bluetooth communication system between two devices, suitable for detecting the position of one of the devices with respect to the other, including in the absence of GPS. The method uses a magnetometer type sensor such as an electronic compass.
U.S. Pat. No. 6,788,199 describes a system for tracking persons, comprising a transmitter-receiver attached to the person to be tracked and a portable tracking device. The latter transmits a tracking signal containing an address code to the transmitter-receiver, which transmits a signal in return if the code is correct. The tracking device using this signal to determine the distance and/or direction of the transmitter-receiver with respect to the tracking device.
U.S. Pat. No. 6,529,131 describes a Bluetooth communication system between two devices (a “master” device and a “slave” device), for detecting the position of one of the devices with respect to the other, in particular for monitoring a child, using data from a GPS. The method uses a magnetometer type sensor such as an electronic compass.
The system described in U.S. Patent Publication No. US 2004/0021569 uses gyroscope and accelerometer data to compute the location of a person, which are transmitted to a master control station, via a wireless communication system. This system operates in a closed structure where GPS signals are not available.
The document GB 2 391 991 describes a wireless system for monitoring children, comprising a device borne by the parent, and a device borne by the child, the two devices communicating with each other by radio waves. The child device is equipped with an electronic compass which shows the child the direction wherein the parent device is located.
U.S. Pat. No. 6,778,902 describes a system for monitoring and tracking persons which is not dependent on a satellite geolocation system, but which is based on a complex method for synchronizing a signal transmitted by the monitoring unit to the monitored unit.
U.S. Pat. No. 7,110,777 describes a system for tracking the movement of an object comprising an accelerometer, an external tracking transmitter-receiver, a processing element, and a radio (RF) transmitter-receiver. The system also comprises a mobile monitor which comprises a processing element and an RF transmitter-receiver. This system is suitable for use in zones where GPS signals are not available.
U.S. Pat. No. 7,667,646 (Nokia) describes a system for determining the direction with respect to a target on the basis of the position of a wireless communication device.
U.S. Patent Publication No. US2008085678 describes a mobile monitoring system for tracking persons, the system comprising: one or a plurality of transmission units having an electrical power supply, an RF circuit, and an RF transmission capability inside a portable enclosure, a mobile reception unit including an electrical power supply, an RF reception circuit, and a user interface, wherein said transmission units transmit RF signals to said reception unit such that the position of each transmission unit can be identified with respect to said portable reception unit. The RF transmission can be a Bluetooth transmission. Several other documents describe the use of Bluetooth technology for enabling communication between the monitor device and a monitored device, but without using information from a compass, a gyroscope or an accelerometer for determining the direction of displacement: these are the documents EP 1 699 183 (Broadcom), DE 102005057578, WO 2010/026566, EP 2 509 343 (Nokia), DE 202013000840.
U.S. Pat. No. 5,289,163 (Perez) describes a tracking system for detecting if the child leaves a predetermined perimeter, and for determining the distance and direction wherein the child is located. The determination of the direction is based on an antenna array. U.S. Pat. No. 6,344,797 also describes the use of antennas for tracking.
Further similar systems based on the exchange of radiofrequency signals are described in U.S. Pat. No. 5,900,817, U.S. Pat. No. 6,078,260 (Sony) and U.S. Patent Publication No. 20030034894.
Moreover, it is known that protocols for tracking a transmitter by means of a received signal strength measurement of an antenna do not enable, as is, sufficiently precise tracking to estimate the distance in sensor arrays (see the publication “De la pertinence du RSSI pour la localisation dans les réseaux de capteurs” by Karel Heurtefeux and Fabrice Valois, published in AlgoTel, May 2012, La Grande Motte, France, <hal-00690748>).
An unsolved problem is the precise tracking (within a typical distance of 100 meters), in a Cartesian plane, of an object in movement equipped with a specific device using a mass-market device (such as a Smartphone), in turn possibly in movement; this tracking being performed independently of the external networks to which these two devices are connected (Wi-Fi base, GPS, GSM, etc.).
The problem that the present invention aims to solve is that of providing a device and method for near-field tracking of an object in continuous or intermittent movement, this near-field tracking extending over a range not exceeding some hundreds of meters and involving the determination of the exact coordinates in a Cartesian plane, of a first object, which can be situated in an open (i.e. outdoors) or closed (i.e. in a building) space using a second object, a reference frame of said Cartesian plane.
More particularly, the objects or subjects in continuous or intermittent movement may be a child or a pet or any other animate or inanimate objects.